1. Field of the Invention
This invention relates to a method of etching semiconductor wafers.
2. Description of the Related Art
A conventional method for etching semiconductor wafers, which is illustrated in FIG. 6, involves coating protective resist 35 on pattern surface 39 of semiconductor wafer 34. Protective film 37 is coated on sections other than those requiring etching on etching surface 38, and alumina plate 36 is adhered on pattern surface 39 via protective film 37. Then etching is performed and a thin section (not shown in the Figure) is formed on a diaphragm, etc., of the etching surface 38.
In the conventional etching method, each manufacturing step represented by process (a) to (f) in FIG. 7 is performed. First, in protective resist application step (a), protective resist 35 is coated on pattern surface 39 in order to prevent pattern surface 39 of semiconductor wafer 34 from being scratched.
Next, in alumina plate application step (b), alumina plate 36 is heated with a hot plate, etc., and solid petroleum protection wax is heated and melted, and spread over the alumina plate 36. Then, pattern surface 39 side is directed toward the alumina plate 36 side, and set so that semiconductor wafer 34 is pressed thereon. The melted petroleum protection wax is then applied in the same manner to the circumference of semiconductor wafer 34.
Etching surface 38 is alkali-etched in etching step (c). When the alkali etching is completed, the semiconductor wafer is reheated with a hot plate, or other type of heating device, in alumina plate removal step (d) in order to remove unnecessary alumina plate 36.
In wax cleaning step (e), the petroleum protection wax adhered to the semiconductor wafer 34 is cleaned off with trichloroethane. Finally at resist peeling step (f), the protective resist 35 is peeled and cleaned off with a solvent such as FUJI HUNT MS1001 and trichloroethane.
With the above-described conventional semiconductor wafer etching method, as the protective film 37 is formed by heating and melting the petroleum protection wax, which is solid at room temperature, the steps of applying an alumina plate (b) and removing the alumina plate (d) are performed. When the semiconductor wafer 34 is pressed against the alumina plate 36 as the alumina plate 36 is applied thereto in step (b), the roughness of the surface of alumina plate 36 affects pattern surface 39 of the semiconductor wafer 34, which could result in pattern surface 39 being scratched. Therefore, protective resist 35 must be used in order to prevent scratches. Protective film 37 and protective resist 35 are peeled off and cleaned after etching, but the trichloroethane used as the peeling solvent for both items must have an outstanding cleaning efficiency. Due to the fact that increased attention is being paid to global environmental pollution, and especially as the destruction of the ozone layer is becoming a worldwide problem, the use of trichloroethane has been limited with fluorocarbons as an ozone-destruction organic substance (chlorine solvent), and thus, future use will not be possible.
Therefore, with conventional technology, complete peeling and cleaning of the protective resist 35 and protective film 37 will not be possible.